1. Field of the Invention
The invention relates to an eccentric shaft having at least one counterweight which is arranged to be keyed to the shaft as a separate part.
It also relates to the use of such an eccentric shaft as the drive shaft of a displacement machine of the spiral type of construction.
2. Discussion of Background
Displacement machines of the spiral type of construction having such an eccentric shaft are known, for example, from DE-A-3 313 000. A compressor constructed in accordance with this principle is characterized by an almost pulsation-free delivery of the gaseous working medium consisting, for example, of air or of an air/fuel mixture and could therefore also be advantageously used for, among other things, purposes of charging internal combustion engines. During the operation of such a compressor, several approximately sickle-shaped working spaces are enclosed along the displacement chamber between the spiral displacement body and the two circumferential walls of the displacement chamber, which spaces move from the inlet through the displacement chamber towards the outlet with continuous reduction in their volume and corresponding increase in the pressure of the working medium.
In this known machine, two eccentric arrangements arranged at a distance from one another are provided, one of which can be driven via a drive shaft. This results in a statically determined bearing arrangement which, in addition, ensures positive guidance of the rotor apart from the top and bottom dead centers of the rotor position. To achieve unambiguous guidance of the rotor also at the dead center positions of the rotor, a guide shaft, supported in the housing, of the second eccentric arrangement is force-locked to the drive shaft via a transmission, the transmission being formed, for example, by a toothed belt drive.
The main shaft driving the rotor is centrally arranged and carries two counterweights which are fitted onto the shaft symmetrically with respect to the center of the eccentric bearing. The angular position of such counterweights is usually achieved by means of a key. In this connection, the determination of the key seating position with respect to the position of the eccentric represents a not inconsiderable problem in manufacture. This is because the prerequisite for a running of the charger without imbalance is a very accurate angular position of the key seating.